Change write() to write_all()
Change write() to write_all()

So that the line will error if, for some reason, the pid is only partially
written. This seems unlikely, but it makes clippy happy, because otherwise
clippy is concerned that we are not checking for the amount written.

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

stratis-storage/stratisd,stratis-storage/stratisd,mulkieran/stratisd,stratis-storage/stratisd,mulkieran/stratisd,trgill/stratisd,trgill/stratisd