Util: fix PyGILState_Check failure in some getters

Yury Matveevrequested to merge
fix-pygilstate_check into develop

Closes issues found by @ajoubertza after !855 (merged):

in Util.get_device_by_name(), Util.get_device_list(), Util.get_device_list_by_class() we got PyGILState_Check failure, due to we tried to fill Pyhton list with relesed GIL. Now we release GIL only for the cppTango core call.

For Util.reset_filedatabase() GIL release was removed completely

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