Make San happy: use Environment.getExternalStorage... instead of hardcoding "/sdcard"

Bug: 2541880
Change-Id: If1714852a6df0f1f399badd4661d3452370e8046
Merge commit '2bd1c8d96e94b95f267234d4aac33f699d678202' into oxygen_4.3

Conflicts:
	apps/BugReportSender/src/com/android/bugreportsender/BugReportListActivity.java