tests: adapt tests to change in pwd's default

tests: adapt tests to change in pwd's default

* tests/misc/pwd-option.sh (base): Initialize with -P,
now that -L is the default, to accommodate an initial
working directory with a symlink component.
* tests/misc/readlink-fp-loop.sh: Use $(env pwd -P) to get the
absolute working directory.  Using "env" ensures we do not invoke
any shell built-in, and PATH ensures we invoke the one from coreutils.
* tests/readlink/can-e.sh: Likewise.
* tests/readlink/can-f.sh: Likewise.
* tests/readlink/can-m.sh: Likewise.