This reverts commit 334f399ee36e1ea1833298c1a72354af001d01aa, reversing
changes made to 45a5d28bad92bef23832fdc88a4806c911c6fc52.
When testing against Windows SSH the Powershell script fails to parse
the newly added if statement.
This change sets the ErrorActionPreference and wraps the script execution in a Try/Catch statement so that the provisioner can capture any errors encountered when running the script. In addition to the try/catch the `&` operator is replaced by the `.` sourcing operator to ensure the script is executed in the same scope as the parent command (so that errors bubble up properly).
Tests after change
```
⇶ ACC_TEST_BUILDERS=amazon-ebs ACC_TEST_PROVISIONERS=powershell go test ./provisioner/powershell/... -timeout=1h
ok github.com/hashicorp/packer/provisioner/powershell 915.865s
```
* Modifies the amazon-ebs builder with a windows build configuration
```
⇶ ACC_TEST_BUILDERS=amazon-ebs ACC_TEST_PROVISIONERS=powershell go test -v ./provisioner/powershell/... -run=TestPowershellProvisioner_Inline
--- PASS: TestPowershellProvisioner_Inline (256.50s)
--- PASS: TestPowershellProvisioner_Inline/testing_amazon-ebs_builder_against_powershell_provisioner (256.50s)
PASS
ok github.com/hashicorp/packer/provisioner/powershell 256.525s
```