mcf: Add sanity check for git mirrors, premirrors and sstatemirrors (v4.0.6)
mcf: Add sanity check for git mirrors, premirrors and sstatemirrors (v4.0.6)

:Release Notes:
Show warning when:
 * .gitmirror isn't used
 * one of sstatemirror options points to non-existent or empty dir
 * premirror points to non-existent or empty dir

:Detailed Notes:

:Testing Performed:
Only build tested.

:QA Notes:
No change to image.

:Issues Addressed:
[ES-441] mcf needs to check that --premirror and --sstatemirror
         arguments are mounted
[ES-497] mcf should add (or offer to add, or warn if missing) the
         git-mirror settings

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I5cb6f24d140ea6680875e3a336c6b1c7bcb3a921
Reviewed-on: https://g2g.palm.com/4992
Reviewed-by: DCO Verification
Build: Martin Jansa <516df3ff67e1fa5d153800b15fb204c0a1a389dc@lge.com>
Reviewed-by: Martin Jansa <516df3ff67e1fa5d153800b15fb204c0a1a389dc@lge.com>
Tested-by: Martin Jansa <516df3ff67e1fa5d153800b15fb204c0a1a389dc@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Susan Montooth <be0b8b1fe2cc6a744be9b1ae6516e077aa323e09@lge.com>

aeg-aeg/mywebOS,openwebos/build-webos,openwebos/build-webos,hyunkim9123/build-webos,hyunkim9123/build-webos,aeg-aeg/mywebOS