dumpstate: execute procrank using su

procrank is a setuid binary which only exists on userdebug/eng
builds. Instead of executing the setuid binary, run the binary using
the su command. This eliminates one more setuid binary, and allows
the tightening of the SELinux policy.

Bug: 18342188
Change-Id: I81d06196a29489feaefb2fea0cf5c4ff1e273d2f