fix some dialyzer issues

[zdaniel86]

Problem Description

Dependent project suffers from dialyzer issues such as:
src/erl_cache.erl:156: The call erl_cache:validate_opts(CacheOpts::any(),[]) will never return since it differs in the 2nd argument from the success typing arguments: (any(),'undefined') src/erl_cache.erl:157: The pattern {'ok', ValidatedOpts} can never match the type {'error',{'invalid','cache_name'}} src/erl_cache.erl:202: The pattern {'ok', ValidatedOpts} can never match the type {'error',{'invalid','cache_name'}} src/erl_cache.erl:229: The pattern {'ok', ValidatedOpts} can never match the type {'error',{'invalid','cache_name'}} src/erl_cache.erl:252: The pattern {'ok', ValidatedOpts} can never match the type {'error',{'invalid','cache_name'}} src/erl_cache.erl:300: The call erl_cache:validate_opts(Opts::any(),[]) will never return since it differs in the 2nd argument from the success typing arguments: (any(),'undefined') src/erl_cache.erl:301: The pattern {'ok', ValidatedOpts} can never match the type {'error',{'invalid','cache_name'}} src/erl_cache.erl:397: The call erl_cache:default(Key::'key_generation',Defaults::[{'error_validity' | 'evict' | 'evict_interval' | 'is_error_callback' | 'key_generation' | 'max_cache_size' | 'mem_check_interval' | 'refresh_callback' | 'validity' | 'wait_for_refresh' | 'wait_until_done',atom() | fun() | non_neg_integer() | {_,_,_}}]) breaks the contract (config_key(),cache_opts()) -> term()

Solution Description

All these issues caused by single type config_key()
This change doesn't touch real functionality. So it can be merged without careful testing. It just makes dialyzer little bit more happy.

[spil-jenkins]

Test PASSed.
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Test PASSed.