Fixing CARBON-14482, Updated to set username to the CarbonContext in CarbonTomcatRealm.

Signed-off-by: Jayanga Dissanayake <jsdjayanga@yahoo.com>
Modifying tests to use a custom valve and removing unwanted dependency from pom.xml

Signed-off-by: Jayanga Dissanayake <jsdjayanga@yahoo.com>
Merging changes from jayanga related to pull#40
Merge branch 'jsdjayanga-master' with pull#40