test: put each arg in a separate string

Each arg to docker run should be placed in a separate string.
Otherwise, when starting the command via exec.Cmd, the command is
interpreted as "echo test", which can't be found.
test: fix TestCreateStartRestartStopStartKillRm

cat needs stdin opened, otherwise it dies immediately.
test: skip TestCreate on Fedora due to lxc utils bug

In the dind environment running on a Fedora host, the lxc utils get
confused by the /sys/fs/cgroup/cpuacct,cpu cgroup mount and lxc-start
fails trying to access the wrong cgroup directory.
test: 2 second timeout (not 2000)
test: fix TestRmi race condition
test: remove extra args in TestExitCode

The extra blank argument isn't needed and confuses libvirt.
Merge pull request #2747 from jpoimboe/test-fixes

Test fixes