[server] fix deserialize_schema to handle properly pg schema (closes 17076486)
Postgres behaviour is to look first for a table in the configured schema then
fall back to 'public' if no table is found.
This must be implemented in deserialize_schema when listing existing tables
to check for computed relations (cw_cwcomputedrtype) otherwise computed
relations may not work when using non-default pg schema.
### Requirements for tests in various cubicweb/**/test directories. ###
## shared by several test folders
cubicweb-card
docutils
Twisted < 16.0.0
webtest
## cubicweb/test
Pygments
mock
#fyzz XXX pip install fails
cubicweb-file
cubicweb-localperms
cubicweb-tag
## cubicweb/devtools/test
flake8
## cubicweb/hooks/test
psycopg2
## cubicweb/pyramid/test
pyramid >= 1.5.0
waitress >= 0.8.9
wsgicors >= 0.3
pyramid_multiauth
## cubicweb/sobject/test
cubicweb-comment