SetFlagsRule: change the default behavior of SetFlagsRule

This commit changes the default behavior of SetFlagsRule from set all
flag value to null to the device value.

Bug: N/A
Test: atest FlagJUnitTests FlagJUnitHostTests
Change-Id: I7fb534f84f756c3a78a625bc0a1ac2be3fb86620
1 file changed