lowmemorykiller: enhance debug information

Add extra debug information to make it easier to both determine
why the lowmemorykiller killed a process and to help find the source
of memory leaks.

Also increase the debug level for "select" statements to help prevent
flooding the log.

Change-Id: I3b6876c5ecdf192ecc271aed3f37579f66d47a08
Signed-off-by: Liam Mark <lmark@codeaurora.org>