Encode URL with parameters for POST

This is a work around for an upstream issue[1] that prevents the ARI from
accepting json via POST.

[1] https://issues.asterisk.org/jira/browse/ASTERISK-22685

Change-Id: Ibc8e2574066fa6225a445e78f115ab1656e91889
Signed-off-by: Paul Belanger <paul.belanger@polybeacon.com>