please add support for multiple gpg servers

[abmpicoli]

Hi, everyone...

First of all, very neat idea of having tomcat native being built within the image.

I'm trying to adapt the tomcat Dockerfile to using an IBM-provided jdk image, that uses ubuntu.

And, so far so good... except for the fracking gpg keys:

I've seen issue #87 closed as no action, with the justification that "the gpg server should be stable"...

Well, the fact is that it isn't. And I don't think this is anything people can control: zombie apocalypse, solar flares, a dog close to the server plug , an intern doing something silly, anything can cause a shortage, that breaks the build. I've tried 4 times the build using only the gpg server provided, and the build failed miserably all the times... I had to add the solution for cycling servers...

Maybe you should consider the same...

export GNUPGHOME="$(mktemp -d)"; \
	for key in $GPG_KEYS; do \
	for server in ha.pool.sks-keyservers.net \
	              hkp://p80.pool.sks-keyservers.net:80 \
	              keyserver.ubuntu.com \
	              hkp://keyserver.ubuntu.com:80 \
	              pgp.mit.edu; do \
								gpg --batch --keyserver "$server" --recv-keys "$key" && break || echo "Trying new server..." ; \
								done ;\
	done; \

[tianon]

See #127, which has pretty well eliminated this problem for us.