Implement set SSL on gateway

[snowch]

PUT /api/v1/install/?install_reconfig HTTP/1.1
Host: 127.0.0.1:8080
Content-Length: 3477
Accept-Encoding: gzip, deflate
REMOTE_ADDR: 109.151.141.70
Accept: */*
User-Agent: python-requests/2.6.0 CPython/2.7.5 Linux/3.10.0-1127.18.2.el7.x86_64
Connection: keep-alive
X-BDS-SESSION: /api/v2/session/d8824c3e-71de-489b-ad07-44d0cf1abc31
Authorization: /api/v2/session/d8824c3e-71de-489b-ad07-44d0cf1abc31

{"gateway_ssl_cert_info": {"cert_file": {"content": "-----BEGIN CERTIFICATE-----XXXX-----END CERTIFICATE-----\n", "file_name": "cert.pem"}, "key_file": {"content": "-----BEGIN RSA PRIVATE KEY-----XXXX-----END RSA PRIVATE KEY-----\n", "file_name": "key.pem"}}}

HTTP/1.1 204 No Content
Access-Control-Allow-Origin: *
Content-Length: 0
Content-Type: text/plain
Date: Mon, 17 Aug 2020 17:37:00 GMT
Server: HPE Ezmeral Container Platform 5.1

[snowch]

See also: #178

[snowch]

Initial functionality: 809c00d