rgw: add insecure option to the http client

rgw: add insecure option to the http client

This allows the http client to turn off ssl certificate peer checking,
which is turned on by default. This is useful in cases like when
Keystone is SSL terminated with a self signed certificate.
The option `rgw_keystone_verify_ssl` (default true) can be toggled if
self signed certs are used, so that swift and s3 apis using keystone
authentication can work.

Fixes: #14583
Reported-by: Karol Mroz <mroz.karol@gmail.com>
Signed-off-by: Abhishek Lekshmanan <abhishek@suse.com>