MULE-6783: HTTP inbound keep-alive attribute not overriding the keepAlive attribute of HTTP connector

_ Managing keep-alive override in endpoint
_ Updating test to check for keep alive in  HTTP 1.0 and 1.1 versions
(cherry picked from commit aa4bbdc)
MULE-6783: HTTP inbound keep-alive attribute not overriding the keepAlive attribute of HTTP connector

_ Removing unused attribute in test connector
(cherry picked from commit c0e9cd4)