detect-environment: Filter the output of env

The detect-environment script is quite noicy due to the fact that it
prints the environment every time it's sourced. Hence, modified it to
print only the environment variables that the script affects.

Ticket: ENT-12600
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

build-scripts/detect-environment

@@ -419,7 +419,7 @@ detect_environment
 echo
 echo
 echo "==================== Current environment ========================"
-env
+env | grep -E "^(label|CROSS_TARGET|UNAME|OS|OS_VERSION|DEP_PACKAGING|PACKAGING|ARCH|MAKE|FUSER|PATCH|MAKEFLAGS)="
 echo "================================================================="
 echo
 echo