cuttlefish launch: fix qemu_gdb flag

Due to an earlier refactoring of the flag code, the parameter passed to
-qemu_gdb was treated as a (relative) path. In that case the example
from the documentation (-qemu_gdb=tcp::1234) was passed as
/your/current/path/tcp::1234.

Restore the original behaviour.

Test: tested in local environment
Change-Id: Ie8180b1a8fce300205f22b6e34108c3e6306dbdd
tree: 18ee155479b8635b94e56eb54464446368419896
  1. common/
  2. guest/
  3. host/
  4. tests/
  5. tools/
  6. Android.bp
  7. Android.mk
  8. OWNERS