GH-111 Provide means for determining if connection is valid.

Implement Connection.isValid(int timeout)
Implement Metadata.isHPCCTargetReachable

Signed-off-by: Rodrigo Pastrana <Rodrigo.Pastrana@lexisnexis.com>
GH-111 Close test connection after use.

Signed-off-by: Rodrigo Pastrana <Rodrigo.Pastrana@lexisnexis.com>
Merge pull request #112 from rpastrana/gh-111-connection-validity

GH-111 Provide means for determining if connection is valid.