cmds: add #!s

Without this, exec()ing these fails.

Found with `grep -L bin/sh $(grep -Rl Script)`

Bug: None
Test: exec()ed each of these scripts; I no longer get "exec format
error" for any of them.
Change-Id: I47db5007e5cc14ab91eb846b7bffecb925d37874
diff --git a/cmds/pm/pm b/cmds/pm/pm
index 8183838..53f85b2 100755
--- a/cmds/pm/pm
+++ b/cmds/pm/pm
@@ -1,3 +1,4 @@
+#!/system/bin/sh
 # Script to start "pm" on the device, which has a very rudimentary
 # shell.
 #