Ubuntu – Unable to load dynamic library ‘/usr/lib/php/20151012/php_xmlrpc.dll’

Dynamic link libraries (DLLs) are a Windows-specific technology and don't work on Ubuntu. Because PHP can be run on different operating systems, its configuration files contain examples for how to configure it on different operating systems:

;;;;;;;;;;;;;;;;;;;;;;
; Dynamic Extensions ;
;;;;;;;;;;;;;;;;;;;;;;

; If you wish to have an extension loaded automatically, use the following
; syntax:
;
;   extension=modulename.extension
;
; For example, on Windows:
;
;   extension=msql.dll
;
; ... or under UNIX:
;
;   extension=msql.so
;
; ... or with a path:
;
;   extension=/path/to/extension/msql.so

Normally, the Linux build of PHP already comes with SSL support built in, in contrast to the Windows build, where you need the DLL you mentioned. But you seem to use a third-party build of PHP 7 (maybe a from PPA?), because Ubuntu 14.04 comes with PHP 5 by default. So this third-party build might handle SSL differently.

You're trying to use a Windows library (a DLL) on a Linux system. DLLs don't work on Linux (apart from emulating with Wine, developing with Mono or such). Additionally, the .dll file you're referencing in your config isn't even there ;)

You need the corresponding .so library, which should be supplied by the package php7.0-soap. In general, many PHP modules can be found in their respective packages, like php7.0-mysql, php7.0-intl or php7.0-cgi.