Fix bug in sysctl module for multivalue values

sysctl failed with the following test case due to the str formatting not
quoting the value.

    - sysctl: name=net.ipv4.tcp_wmem value="4096 65536 16777216" state=present

For reference this should produce something like this.

    sysctl -w net.ipv4.tcp_wmem="4096 65536 16777216"