Explictly check for stdClass in VariableStore initializer

[smgallo]

Description

Since stdClass objects are not an instance of Traversable and is_traversable() is not available until PHP 7.x we need an explicit check for stdClass when initializing the VariableStore with the contents of variables declared in an action configuration. For example,

"variables": {
   "var1": 10,
   "var2": "some string"
}

Now, an error is properly thrown

Motivation and Context

Previous error:

2019-02-15 00:09:25 [error] (ETL\VariableStore): ETL\VariableStore::__construct() Expected array or VariableStore, got object

Improved error:

2019-02-15 15:09:01 [error] Error verifying sections: ('xdmod.gallo': Error verifying actions: xdmod.gallo.xdmod-public-user ((ETL\VariableStore): Value for bad1 must be scalar, array provided))

Tests performed

Manual tests.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project as found in the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.