Declare mCommitted as AtomicBoolean in PackageInstallerSession

mCommitted is declared as boolean and is accessed with holding mLock.
mCommitted is set to be true only in streamValidateAndCommit(). After
that, the value of mCommitted shouldn't set back to false.

In order to reduce the chance to make a deadlock situation happen,
this patch changes mCommitted declaration from boolean to
AtomicBoolean.

Test: atest \
                CtsStagedInstallHostTestCases \
                CtsPackageInstallTestCases \
                CtsAtomicInstallTestCases
Test: Presubmit Treehugger

Fix: 197088926
Change-Id: I7e7e952e26c07518539a3e3f587f699c7ecef782