limactl: escape only the value of env variables in shell

[sam-berning]

#1482

Testing

$ ./_output/bin/limactl shell default HI=$ env 
HI=$
...

[jandubois]

I feel somewhat uneasy about this change, as it is just a heuristics that works for some cases, but not others. But I guess it is an improvement over the current status, so we should still apply it.

An obvious (and fixable) case is having = characters in the value part, but I feel that you will always be able to create edge cases that cannot be handled by simple mechanisms like this, e.g.

$ cat foo\$bar=baz
echo baz
$ ./foo\$bar=baz
baz
$ ./_output/bin/limactl shell default ./foo\$bar=baz
/bin/bash: line 1: ./foo=baz: No such file or directory

I think I would like to see support extended to having = signs in the value, but otherwise this is probably complex enough.

[jandubois]

Thanks, LGTM