allow --home to still work with "mount home = no"

[DrDaveD]

Description of the Pull Request (PR):

This allows the --home command line option to still work even when "mount home = no" is set in singularity.conf. The comments in singularity.conf don't say anything about this option disabling setting the home directory on the command line, so although this changes functionality, it fixes a bug in the currently documented behavior.

This affects all versions of singularity that I know about, but it was particularly noticed with 2.4.6 because before that some of my users had specified both --bind and --home for the same mapping. With 2.4.6 the duplication was rejected, so the users removed the --bind, and then ran into one site that had set mount home = no, where the --home was silently ignored.

This fixes or addresses the following GitHub issues:

• None

Checkoff for all PRs:

• I have read the Guidelines for Contributing, and this PR conforms to the stated requirements.
• I have added changes to the CHANGELOG and and documentation updates to the singularityware documentation base.
• I have tested this PR locally with a make test
• This PR is NOT against the project's master branch
• I have added myself as a contributor to the contributors's file
• This PR is ready for review and/or merge

Attn: @singularityware-admin

[DrDaveD]

I rebased on the current developement-2.x.

[GodloveD]

@dctrud, @jmstover, @gmkurtzer and I had a convo about this some time ago to determine whether or not this is something we want to do. We determined with @gmkurtzer's input that this was indeed his original intention. Therefore, I propose that we merge.

[GodloveD]

Oh, also, I tested this and it works and the code seems sensible to me as well.

[GodloveD]

Thanks @DrDaveD !