Set id for bugreports after dumpstate increments it.

dumpstate increments system property PROPERTY_LAST_ID when a bugreport
is triggered.

In the old workflow for bugreports, dumpstate used to get triggered
before Shell, and dumpstate would send the 'id' to Shell. Hence Shell
always assumed that it has a known value for 'id', that is why
'id' is declared as a final variable which could be assigned value in
the constructor.

In new workflow using API, the 'id' is incremented after dumpstate gets
triggered. Hence making the following changes:
* Changing 'id' variable to be not final
* Reading 'id' after dumpstate has incremented the system property

Bug: 123617758
Test:  	Build and flash to device.
	Turn on the feature flaggenerate bugreports
	Check the progress and Finish notifications.

Change-Id: I44762190391c128cba135bf0ef795a1ae872dbb7