roomservice: check uniqueness by path, not name

For repos such as hardware/qcom/media-caf we are using the same name
with different branches for different paths.

for eg.
  CyanogenMod/hardware_qcom_media-caf(branch:8994)
   - fetch to : /hardware/qcom/media-caf/8994
  CyanogenMod/hardware_qcom_media-caf(branch:8960)
   - fetch to : /hardware/qcom/media-caf/8960

For such cases roomservice won't pick up a new path
if one already exists.

We should check for unique by target path instead.

Change-Id: I89e561ca9a2d57ede8cf782f431a8e829ea47ee5
Signed-off-by: Arnav Gupta <championswimmer@gmail.com>