Generate fstab from /proc/mounts. Basically like any regular fstab
minus the requirement for the Android fs_mgr_flags. Added a unit
test to confirm that fs_mgr_read_fstab("/proc/mounts") matches the
setmntent("/proc/mounts")+getmntent() content.
As a result, discovered a bug in parse_flags that would report "ro"
if the "rootcontext=..." flag was referenced.
Test: fs_mgr_unit_test
Bug: 109821005
Change-Id: I635ee979e11ee089b09adbedb5f42b6ba78026de
Spans quoted with " are dealt with atomically, and are stripped from
the key/value results when parsing the kernel cmdline.
Test: compile, device boot, fs_mgr_unit_test
Bug: 109821005
Change-Id: I45f3d7395f34295edefdeaafa4c15c6ee25cc4da