Change nmcli to use XDG_DATA_HOME instead of HOME

Right now nmcli saves its history into ~/.nmcli-history. This would
change it so that it stores it in XDG_DATA_HOME (i.e.
~/.local/share/nmcli-history for most users).
17 jobs for ep/follow-xdg-spec in 38 minutes and 56 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Test
passed #2179857
checkpatch

00:01:45

manual #2179864
allowed to fail manual
t_centos:7.5.1804
manual #2179865
allowed to fail manual
t_centos:7.6.1810
manual #2179871
allowed to fail manual
t_debian:10
manual #2179870
allowed to fail manual
t_debian:9
manual #2179873
allowed to fail manual
t_debian:sid
manual #2179872
allowed to fail manual
t_debian:testing
manual #2179858
allowed to fail manual
t_fedora:28
manual #2179859
allowed to fail manual
t_fedora:29
manual #2179860
allowed to fail manual
t_fedora:30
passed #2179861
t_fedora:31

00:38:56

manual #2179862
allowed to fail manual
t_fedora:32
manual #2179863
allowed to fail manual
t_fedora:rawhide
manual #2179866
allowed to fail manual
t_ubuntu:16.04
manual #2179867
allowed to fail manual
t_ubuntu:18.04
manual #2179869
allowed to fail manual
t_ubuntu:devel
manual #2179868
allowed to fail manual
t_ubuntu:rolling