Replacing ini_get instances with inigetwrapper usages

resolves https://github.com/owncloud/core/issues/11074
For reference:
```
$ php -dmemory_limit=3T -r "str_repeat('foobarbraz', 123456789);"
PHP Fatal error:  Allowed memory size of 262144 bytes exhausted (tried to allocate 1234567891 bytes) in Command line code on line 1
```