Get all projects from ProjectCache instead of GitRepositoryManager

SubmoduleSectionParser was using GitRepositoryManager list method to get
all the projects. According to the inline comment in the list method
implementation in LocalDiskRepositoryManager, this method should only be
called when the cache was flushed by the administrator.

Every time the SubmoduleSectionParser was parsing the sections to find
submodule subscription, it was scanning the file system to find all the
projects.

Change-Id: I745e780e200cf5f4a245c3a08feb18fe7be150a7
2 files changed