base: get rid of android time class

Time is deprecated and sometimes doesn't compute correctly the time using
the normalize function. Replace it in the NetworkPolicyManager for
a GregorianCalendar to ensure the next and last cycle boundaries
are calculated correctly.

Change-Id: I25362a6f61a9bfdbf005c81c97ece9c3e57736ff
JIRA: CYAN-7119
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>