intg: Generate tmp dir with lowercase
This is a workaround for buggy python-requests 2.12.4.
It cannot handle uppercase letters in file path.
The manual page MKTEMP(1) says that the parameter --dry-run is unsafe.
It is not critical for our use-case in CI but we should revert the patch
after fixed version of puython-request will be released
Reviewed-by: Jakub Hrozek <email@example.com>