Prealloc requests fail

[cg2v]

Expected Behavior

sending a preallocate request should allocate the execution slots and return a successful result

Actual Behavior

The slots are allocated, but the request fails with an internal server error.

tornado.application|Uncaught exception POST /prealloc/[KEY]/[image]/[count]/ (::1)
HTTPServerRequest(protocol='http', host='localhost:3000', method='POST', uri='/prealloc/[KEY]/[image]/[count]/', version='HTTP/1.1', remote_ip='::1')
Traceback (most recent call last):
File "/usr/local/lib64/python3.9/site-packages/tornado/web.py", line 1786, in _execute
result = await result
File "/usr/local/lib/Tango/restful_tango/server.py", line 124, in post
instances = await tangoREST.prealloc(key, image, num, self.request.body)
TypeError: object dict can't be used in 'await' expression
tornado.access|500 POST /prealloc/[KEY]/[image]/[count]/ (::1) 14397.99ms

Steps to Reproduce the Behavior

on the tango server:
tango-cli.py -k [KEY] --prealloc --num [count] --image [image] --vmms localDocker

[damianhxy]

The fix should be to make the prealloc method in tangoREST.py async