NativeMediaDrmClearkeyTest: convert "file://" URL to fd

Work around for b/168548052.

Bug: 168529878
Bug: 168548052
Test: atest NativeMediaDrmClearkeyTest -- \
    --module-arg CtsMediaTestCases:instrumentation-arg:media-path:=<media-path> \
    --module-arg CtsMediaTestCases:images-only:false \
    --module-arg CtsMediaTestCases:push-all:true
Change-Id: Ib4ad10a2e277a2b1bb7994a4171bd32c8567346b
1 file changed