False success and missing explanation when plugin PHP requirement isn't met

[holtjohnson]

Describe the current, buggy behavior

When trying to activate a plugin on a server with a PHP version that doesn't meet the plugin's minimum PHP version requirement a vague warning is issued and the plugin isn't activated, but the command exits with a success message.

Describe how other contributors can replicate this bug

This issue isn't specific to PHP 7.1, but we'll use it for demo purposes.

1. Ensure you're running a server with PHP 7.1 or less
2. Run wp plugin install blob-mimes
3. Run wp plugin activate blob-mimes
4. Observe Warning: Could not activate the 'blob-mimes' plugin., but lacking notice of outdated PHP
5. Also observe the incorrect and confusing message displayed: Success: Activated 1 of 1 plugins.

Example from a server running PHP 7.1:

$ wp plugin activate blob-mimes
Warning: Could not activate the 'blob-mimes' plugin.
Success: Activated 1 of 1 plugins.

Describe what you would expect as the correct outcome

I expect running wp plugin activate blob-mimes to give me the same notice the /wp-admin/ area gives when I try to activate a plugin on an outdated PHP version (Error: Current PHP version does not meet minimum requirements for Lord of the Files: Enhanced Upload Security.) and then exit with an error.

I would expect output to look something to this:

$ wp plugin activate blob-mimes
Warning: Current PHP version does not meet minimum requirements for plugin 'blob-mimes'.
Error: No plugins activated.

Let us know what environment you are running this on

OS:	Linux info 3.0 #1337 SMP Tue Jan 01 00:00:00 CEST 2000 all GNU/Linux Linux info 3.0 #1337 SMP Tue Jan 01 00:00:00 CEST 2000 all GNU/Linux Linux info 3.0 #1337 SMP Tue Jan 01 00:00:00 CEST 2000 all GNU/Linux Linux info 3.0 #1337 SMP Tue Jan 01 00:00:00 CEST 2000 all GNU/Linux
Shell:	/bin/bash
PHP binary:	/usr/bin/php7.1-cli
PHP version:	7.1.33
php.ini used:	/etc/php7.1/php.ini
WP-CLI root dir:	phar://wp-cli.phar/vendor/wp-cli/wp-cli
WP-CLI vendor dir:	phar://wp-cli.phar/vendor
WP_CLI phar path:	/homepages/32/d409718396/htdocs/theme-template
WP-CLI packages dir:	/kunden/homepages/32/d409718396/htdocs/.wp-cli/packages/
WP-CLI global config:	/kunden/homepages/32/d409718396/htdocs/.wp-cli/config.yml
WP-CLI project config:
WP-CLI version:	2.4.0

[holtjohnson]

Thanks for your work in addressing this issue so quickly @schlessera and @swissspidy, I appreciate it!