Rename APEX installPackage method to stagePackage.

Test: adb install apex.test.apex  (succeeds)
Bug: 112669193

Merged-In: I8dc23d9d621d6a9fd5ee983eb6edbbe5ed13ad9a
Change-Id: I8dc23d9d621d6a9fd5ee983eb6edbbe5ed13ad9a
1 file changed