[feature request] add ability to purge node

[shantanugadgil]

ref: https://www.nomadproject.io/api/nodes.html#purge-node

my idea was that it could be done using the ID or all 'node name', with possible capability of regex.

use case: after mucking around with data_dir I ended up with duplicate node entries.

for now I am making do using a shell script! 😄