testapp: add pidfile existence check before killing mupd8 and messageserver processes
pom.xml: lower the required version of Maven to 2.2.0

No features in Mupd8 seem to depend on Maven 3.3.0.  This fix lower the required/minimum version.
testapp: add exit code for stop routine

This patch adds exit code 0/1 to 'testapp.h stop' routine.
Merge pull request #19 from zheguang/pull-request-testpp-pom

testapp & pom: add testapp file check & change required maven version