Minor improvements in the bugreport progress workflow:

- Allow users to rename the suffix in the bugreport files by setting the
  dumpstate.pid.name system property. For example, instead of
  bugreport-2015-12-02-15-23-46, it could be bugreport-My-App-Crashed.

- Dynamically adjust the max weight if the current progress overflows
  the previous max (and set the dumpstate.pid.max system property
  accordingly, so UI can be updated as well).

- Strip .txt from the name sent on BUGREPORT_STARTED.

BUG: 25794470
Change-Id: I7634ddd2975bcf93d6612d16c09da1cd7b4e1d91