Databases and java pester tests (#2338)

* added mongodb postgres java tests

* fixed 1.7 and 12 Java on Ubuntu 20

* several improvments

* removed update-environment function

* add etc-environment import

* removed sourcing invoke-tests

Co-authored-by: Leonid Lapshin <originalnoe-nazvanie@yandex.ru>

images/linux/scripts/helpers/Common.Helpers.psm1

@@ -54,4 +54,8 @@ function Get-AndroidPackages {
     $androidSDKManagerPath = "/usr/local/lib/android/sdk/tools/bin/sdkmanager"
     $androidPackages = & $androidSDKManagerPath --list --verbose
     return $androidPackages
+}
+
+function Get-EnvironmentVariable($variable) {
+    return [System.Environment]::GetEnvironmentVariable($variable)
 }