The issue is caused by the fact that this class javax/el/ELManager is introduced in el-api version 3.0.
Tomcat 7 is coming with pre-bundled el-api 2.2 (which is missing the class) and it's picking that at runtime, instead of your el-api jar.
Tomcat 8 has the el-api 3.0 and hence the javax/el/ELManager class is present.
It's best if you can sync your dev/test/prod environments as close as possible.
It makes much more sense to develop against Tomcat 8 in dev, when your test environment has Tomcat 8. As you found out Tomcat 7 and 8 servers comes with different set of libraries, so your code can behave differently against those different set of libraries.
