[SPARK-12504][SQL] [Backport-1.6] Masking credentials in the sql plan explain output for JDBC data sources.

[sureshthalamati]

Currently credentials in JDBC URL/properties for jdbc data sources are included in the explain output. This fix removes credentials from the explain output and show only database table information.

Backporting fix to 1.6 from 2.0 as discussed in PR #10452

CC @marmbrus

[SparkQA]

Test build #2355 has finished for PR 10669 at commit 212b4db.

• This patch fails SparkR unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #2356 has finished for PR 10669 at commit 212b4db.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #2357 has finished for PR 10669 at commit 212b4db.

• This patch fails SparkR unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[sureshthalamati]

retest this please.

sparkR tests are passing in my branch. And also failed tests in the jenkins is not related to the changes in this PR.
@marmbrus

[gatorsmile]

retest this please

[AmplabJenkins]

Can one of the admins verify this patch?

[sureshthalamati]

It did not make it to 1.6 closing the PR.