Merge branch 'ld/p4-cleanup-processes'

p4 updates.

* ld/p4-cleanup-processes:
  git-p4: avoid leak of file handle when cloning
  git-p4: check for access to remote host earlier
  git-p4: cleanup better on error exit
  git-p4: create helper function importRevisions()
  git-p4: disable some pylint warnings, to get pylint output to something manageable
  git-p4: add P4CommandException to report errors talking to Perforce
  git-p4: make closeStreams() idempotent