Add --deqp-screen-rotation=unspecified cmdline flag.

Add --deqp-screen-rotation=unspecified cmdline flag.

On Android dEQP always sets screen orientation to some known value,
which prevents failures / test run aborts due to screen configuration
changes. This is almost always desired but in some situations user may
want to avoid that. This change adds 'unspecified' value, which means
that the application doesn't request any specific orientation and
the system can freely choose it and even change it during test
execution.

Default value for --deqp-screen-rotation remains '0'.

Change-Id: I3e95213cc12a995ec43912c86a0ab9a01c456920