env/linux-x86-sid: add a Python 3 dependency

Needed for LUCI, and not implicitly installed. Though it turned out that
the python3 package on sid gets Python 3.13, and the latest swarming bot
version wasn't compatible with it, so use the python3.12 package for now.

Drop the 'mkdir --mode=0700 /run/sshd' call, SSH still works without it
and so it doesn't seem to be needed anymore. Keeping it can result in a
different error:

	Step 6/9 : RUN mkdir --mode=0700 /run/sshd
	 ---> Running in 47cf43748881
	mkdir: cannot create directory '/run/sshd': File exists
	The command '/bin/sh -c mkdir --mode=0700 /run/sshd' returned a non-zero code: 1

Install nano for minimal interactive debugging convenience while here.

For golang/go#61112.

Change-Id: I9ce538a9fe47d25988bddf879802ebe806b7eaff
Reviewed-on: https://go-review.googlesource.com/c/build/+/665016
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>

Author: dmitshur

env/linux-x86-bookworm/Dockerfile

@@ -52,6 +52,7 @@ ENV DEBIAN_FRONTEND noninteractive
 # lsof: misc basic tool
 # make: used for setting up benchmarks in the x/benchmark builders
 # mercurial: mercurial VCS supported by cmd/go
+# nano: for interactive debugging convenience
 # netbase: for net package tests, issue 42750
 # patch: used for building some benchmarks
 # procps: misc basic tool

env/linux-x86-bullseye/Dockerfile

@@ -26,6 +26,7 @@ ENV DEBIAN_FRONTEND noninteractive
 # lsof: misc basic tool
 # make: used for setting up benchmarks in the x/benchmark builders
 # mercurial: mercurial VCS supported by cmd/go
+# nano: for interactive debugging convenience
 # netbase: for net package tests, issue 42750
 # patch: used for building some benchmarks
 # procps: misc basic tool

env/linux-x86-sid/Dockerfile

@@ -18,6 +18,8 @@ ENV DEBIAN_FRONTEND noninteractive
 # libgles2-mesa-dev libopenal-dev fonts-droid-fallback: required by x/mobile repo
 # upx: executable compressor, needed to test for go binaries compatibility
 # qemu-user: QEMU (machine emulator and virtualizer) user-space emulation
+# python3.12: for bootstrapswarm
+# nano: for interactive debugging convenience
 RUN apt-get update && apt-get install -y \
 	--no-install-recommends \
 	libcrypt1 \
@@ -44,10 +46,32 @@ RUN apt-get update && apt-get install -y \
 	make \
 	sudo \
 	iproute2 \
+	python3.12 \
+	nano \
 	&& rm -rf /var/lib/apt/lists/*
 
-# Otherwise we get "Missing privilege separation directory: /run/sshd" ...
-RUN mkdir --mode=0700 /run/sshd
+# bootstrapswarming requires a 'python3' binary in PATH, so add one that points to the python3.12 installed above.
+#
+# Note: python3.12 is installed because python3 gets python 3.13, and as of 2025-04-16 swarming bot wasn't compatible
+# with it due to reliance on a deprecated 'pipes' module:
+#
+#	2025-04-16 00:10:05.187 E: Failed to run start_bot
+#	Traceback (most recent call last):
+#	  File "/home/swarming/.swarming/swarming_bot.1.zip/__main__.py", line 324, in main
+#	    return fn(args)
+#	  File "/home/swarming/.swarming/swarming_bot.1.zip/__main__.py", line 194, in CMDstart_bot
+#	    from bot_code import bot_main
+#	  File "/home/swarming/.swarming/swarming_bot.1.zip/bot_code/bot_main.py", line 47, in <module>
+#	    from api import bot
+#	  File "/home/swarming/.swarming/swarming_bot.1.zip/api/bot.py", line 20, in <module>
+#	    from api import os_utilities
+#	  File "/home/swarming/.swarming/swarming_bot.1.zip/api/os_utilities.py", line 24, in <module>
+#	    import pipes
+#	ModuleNotFoundError: No module named 'pipes'
+#
+# Once swarming bot is updated to be compatible with the latest python3 version, this can be removed
+# and the python3 package can be installed.
+RUN ln -s /usr/bin/python3.12 /usr/local/bin/python3
 
 RUN mkdir -p /go1.4-amd64 \
 	&& ( \