Merge pull request #3515 from robertcv/enh/multiple_databasees

[MNT] Tests: add support for multi-database tests

.travis.yml

@@ -2,6 +2,9 @@ language: python

dist: xenial

services:
  - docker

matrix:
    include:
        - env: RUN_PYLINT=true

.travis/install_mssql.sh

@@ -0,0 +1,7 @@
sudo docker run -e 'ACCEPT_EULA=Y' -e 'SA_PASSWORD=YourStrong!Passw0rd' \
   -p 1433:1433 -d microsoft/mssql-server-linux:2017-latest

export PYMSSQL_BUILD_WITH_BUNDLED_FREETDS=1
pip install pymssql

export ORANGE_TEST_DB_URI="${ORANGE_TEST_DB_URI}|mssql://SA:YourStrong!Passw0rd@0.0.0.0:1433"

.travis/stage_install.sh

@@ -4,6 +4,7 @@
for script in \
    install_orange.sh    \
    install_postgres.sh  \
    install_mssql.sh    \
    install_pyqt.sh
do
    foldable source $TRAVIS_BUILD_DIR/.travis/$script

Orange/data/sql/table.py

@@ -75,8 +75,8 @@ def __init__(
                try:
                    self.backend = backend(connection_params)
                    break
                except BackendError as ex:
                    print(ex)
                except BackendError:
                    pass
            else:
                raise ValueError("No backend could connect to server")
        else: