sbox: print failing command line before output

The full command line run inside sbox can be very long, and printing it
after the errors printed by the failing command can hide the error
messages.  Buffer the output of the command and print the failing command
line before the output if it fails.

Bug: 185516277
Test: m out/soong/.intermediates/frameworks/base/system-api-stubs-docs-non-updatable/android_common/metalava/api_lint.timestamp with lint error
Change-Id: I893f3dd01f1baf195e182111c5c49e92eb82f3b0