monitor: Build only if dependencies have changed.

This CL fixes two issues:
- Fully expanding the path to the libraries (i.e commong -> out/host/../common.jar)
  allows the use of "mm" from sdk/monitor/ folder.
- The target of the build (the monitor script) will now have a timestamp that
  corresponds to when it was last built, as opposed to when the source script was
  last modified. As a result, timestamps of the dependency jar files are correctly
  checked with the last build time of the target.

Change-Id: I77469561d6750d1942cfeda1d6672d6d2a5dad51
1 file changed