Solve one more issue where privilege is required to open a file and
we do not want to grant such to the service. This is the service side
of the picture, android_get_control_file() in libcutils is the client.
The file's descriptor is placed into the environment as
"ANDROID_FILE_<path>". For socket and files where non-alpha and
non-numeric characters in the <name/path> are replaced with _. There
was an accompanying change in android_get_control_socket() to match
in commit 'libcutils: add android_get_control_socket() test'
Add a gTest unit test for this that tests create_file and
android_get_control_file().
Test: gTest init_tests --gtest_filter=util.create_file
Bug: 32450474
Change-Id: I96eb970c707db6d51a9885873329ba1cb1f23140
