Statsd dumpsys handles multiple and saved configs

Statsd dumpsys wasn't handling multiple configs properly. Also, doing a
dump would delete the data that had been saved to disk. This cl fixes
both those issues.

Test: run cts-dev -m CtsStatsdHostTestCases -t android.cts.statsd.atom.HostAtomTests#testDumpsysStats
Change-Id: I5f2f86c70fbcbc1407aae1b1ffeb7fbdb9f67d0e