Unsafe calls to yaml.load

[vmatare]

vcstools/src/vcstools/tar.py

Line 80 in 60fec9b

metadata = yaml.load(metadata_file.read())

vcstools/src/vcstools/tar.py

Line 168 in 60fec9b

metadata = yaml.load(metadata_file.read())

yaml.load is deprecated, and these calls should be replaced with e.g. yaml.safe_load

See https://nvd.nist.gov/vuln/detail/CVE-2017-18342
Cf. ros/ros_comm@29053c4

[tkruse]

I think the same was done in vcstools/wstool#134, and a small PR has high chances of being merged by me.

[dirk-thomas]

Closing since the repository is about to be archived: see #166.