Migrate 'Get Request' (bgpcep)

Migrate 'Get Request' (bgpcep)

There are a couple places in bgpcep test suites where deprecated
'Get Request' RequestsLibrary keyword is used. Replace it with
'GET On Session'.

Also, use 'anything' instead of 'any' and do not remove 'alias=' for
the session argument to make them more consistent across all the test
suites.

JIRA: INTTEST-141
Change-Id: Id8bf71a5477cdfb5d6181016a614bbc8f7dfc083
Signed-off-by: Sangwook Ha <sangwook.ha@verizon.com>