Use PMIX_JOB_SIZE instead of PMIX_UNIV_SIZE

[rgmiller]

The PMIX_UNIV_SIZE value is the number of allocated slots in the job
whereas the PMIX_JOB_SIZE is the number of actual processes that have
been started. When trying to calculate how many instances of unifyfsd
to expect, PMIX_JOB_SIZE is the correct value.

See issue #707

Description

This changes the PMIx init code to use PMIX_JOB_SIZE instead of PMIX_UNIV_SIZE. It also replaces strncpy() with strlcpy() in a few places.

Motivation and Context

See #707

How Has This Been Tested?

Types of changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Testing (addition of new tests or update to current tests)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the UnifyFS code style requirements.
• I have updated the documentation accordingly.
• [ x] I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• [ x] All commit messages are properly formatted.