heapprofd_client: proceed even if unable to read own cmdline + move std::string usage
heapprofd_client: proceed even if unable to read own cmdline + move std::string usage

The argv construction should have never been between the fork & exec.

Change-Id: I34a44cbbaf32b70abf58dedfaef8b503ae9de649
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto