[Ubuntu] Implement first Pester tests (#2270)

* implement first pester tests

* add comment for azcopy test

* remove extra importing and old function

* resolve comments

* fix typo

images/linux/scripts/installers/7-zip.sh

@@ -4,13 +4,11 @@
 ##  Desc:  Installs 7-zip
 ################################################################################
 
+source $HELPER_SCRIPTS/invoke-tests.sh
+
 # Install 7-Zip
 apt-get update -y
 apt-get install -y p7zip p7zip-full p7zip-rar
 
 # Run tests to determine that the software installed as expected
-echo "Testing to make sure that script performed as expected, and basic scenarios work"
-if ! command -v 7z; then
-    echo "7-Zip was not installed"
-    exit 1
-fi
+invoke_tests "Tools" "7-Zip"

images/linux/scripts/installers/azcopy.sh

@@ -4,6 +4,8 @@
 ##  Desc:  Installs AzCopy
 ################################################################################
 
+source $HELPER_SCRIPTS/invoke-tests.sh
+
 # Install AzCopy7
 wget -O azcopy.tar.gz https://aka.ms/downloadazcopylinux64
 tar -xf azcopy.tar.gz
@@ -17,13 +19,4 @@ mv /tmp/azcopy /usr/local/bin/azcopy10
 chmod +x /usr/local/bin/azcopy10
 
 # Run tests to determine that the software installed as expected
-echo "Testing to make sure that script performed as expected, and basic scenarios work"
-if ! command -v azcopy; then
-    echo "azcopy7 was not installed"
-    exit 1
-fi
-
-if ! command -v azcopy10; then
-    echo "azcopy10 was not installed"
-    exit 1
-fi
+invoke_tests "Tools" "azcopy"