default student's country to educator's during reg

Ideally the classroom info would include the country code, not just the
country name. Since it doesn't, this change includes a new function to
look up a country code by the country's name (not label).

src/components/registration/steps.jsx

@@ -453,7 +453,7 @@ class DemographicsStep extends React.Component {
     handleChooseGender (name, gender) {
         this.setState({otherDisabled: gender !== 'other'});
     }
-    // look up country name using user's country code selection
+    // look up country name using user's country code selection ('us' -> 'United States')
     getCountryName (values) {
         if (values.countryCode) {
             const countryInfo = countryData.lookupCountryInfo(values.countryCode);
@@ -463,6 +463,12 @@ class DemographicsStep extends React.Component {
         }
         return null;
     }
+    // look up country code from country label ('United States' -> 'us')
+    // if `countryName` is not found, including if it's null or undefined, then this function will return undefined.
+    getCountryCode (countryName) {
+        const country = countryData.countryInfo.find(countryItem => countryItem.name === countryName);
+        return country && country.code;
+    }
     handleValidSubmit (formData) {
         const countryName = this.getCountryName(formData);
         if (countryName && formData.user) {
@@ -573,7 +579,7 @@ class DemographicsStep extends React.Component {
                             validations={{
                                 countryVal: values => this.countryValidator(values)
                             }}
-                            value={countryOptions[0].value}
+                            value={this.getCountryCode(this.props.countryName) || countryOptions[0].value}
                         />
                         <Checkbox
                             className="demographics-checkbox-is-robot"
@@ -598,6 +604,7 @@ class DemographicsStep extends React.Component {
 DemographicsStep.propTypes = {
     activeStep: PropTypes.number,
     birthOffset: PropTypes.number,
+    countryName: PropTypes.string, // like 'United States', not 'US' or 'United States of America'
     description: PropTypes.string,
     intl: intlShape,
     onNextStep: PropTypes.func,

src/views/studentregistration/studentregistration.jsx

@@ -132,6 +132,7 @@ class StudentRegistration extends React.Component {
                             onNextStep={this.handleAdvanceStep}
                         />
                         <Steps.DemographicsStep
+                            countryName={this.state.classroom && this.state.classroom.educator.profile.country}
                             description={this.props.intl.formatMessage({
                                 id: 'registration.studentPersonalStepDescription'
                             })}