[Ubuntu] Prepend brew directories to the PATH (#1168)

* prepend

* add comment and move installation

* change toolcache dir in aws-sam script

images/linux/scripts/installers/aws-sam-cli.sh

@@ -16,7 +16,7 @@ tar -xzvf $TarballPath -C /tmp
 cd /tmp/awslabs-aws-sam-cli*
 
 # Use python 3.7 from toolcache to install aws sam, setuptools package required for the installation
-Python3Dir=$(echo ${AGENT_TOOLSDIRECTORY}/Python/3.7*/x64)
+Python3Dir=$(echo /opt/hostedtoolcache/Python/3.7*/x64)
 Python3BinDir="${Python3Dir}/bin"
 export PATH="$Python3Dir:$Python3BinDir:$PATH"
 python3 -m pip install setuptools

images/linux/scripts/installers/homebrew-validate.sh

@@ -8,7 +8,7 @@
 echo "Validate the Homebrew can run after reboot"
 
 if ! command -v brew; then
-    echo "brew cat not run after reboot"
+    echo "brew executable not found after reboot"
     exit 1
 fi
 

images/linux/scripts/installers/homebrew.sh

@@ -2,6 +2,7 @@
 ################################################################################
 ##  File:  homebrew.sh
 ##  Desc:  Installs the Homebrew on Linux
+##  Caveat: Brew MUST NOT be used to install any tool during the image build to avoid dependencies, which may come along with the tool
 ################################################################################
 
 # Source the helpers
@@ -20,7 +21,7 @@ sudo chmod -R o+w $HOMEBREW_PREFIX
 brew shellenv|grep 'export HOMEBREW'|sed -E 's/^export (.*);$/\1/' | sudo tee -a /etc/environment
 # add brew executables locations to PATH
 brew_path=$(brew shellenv|grep  '^export PATH' |sed -E 's/^export PATH="([^$]+)\$.*/\1/')
-appendEtcEnvironmentPath "$brew_path"
+prependEtcEnvironmentPath "$brew_path"
 
 # Validate the installation ad hoc
 echo "Validate the installation reloading /etc/environment"