[LIVY-398][DOC] Update rest API to reflect the changes of shared context session
[LIVY-398][DOC] Update rest API to reflect the changes of shared context session

LIVY-194 changes the semantics of session in Livy and add supports of shared context for Livy session, so here change the docs in REST API to reflect the changes of LIVY-194.

Author: jerryshao <sshao@hortonworks.com>

Closes #47 from jerryshao/LIVY-398.

meisam/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy