Upgrade to Ehcache 3

I saw on twitter the reference of an article (in french):
http://javaetmoi.com/2016/08/migrer-vers-spring-boot/

That article concludes with something along the lines of  "Besides the
EhCache and Maven configuration, Petclinic does not hold a single line
of XML anymore".

Looking at the code, we can remove more XML if you want. This PR migrates
the cache infrastructure to EhCache 3 and JCache (JSR-107). This also
reduces the number of dependencies.

src/main/java/org/springframework/samples/petclinic/config/CacheConfig.java

@@ -1,6 +1,19 @@
 package org.springframework.samples.petclinic.config;
 
+import java.util.concurrent.TimeUnit;
+import javax.cache.CacheManager;
+
+import org.ehcache.config.CacheConfiguration;
+import org.ehcache.config.builders.CacheConfigurationBuilder;
+import org.ehcache.config.builders.ResourcePoolsBuilder;
+import org.ehcache.config.units.EntryUnit;
+import org.ehcache.expiry.Duration;
+import org.ehcache.expiry.Expirations;
+import org.ehcache.jsr107.Eh107Configuration;
+
+import org.springframework.boot.autoconfigure.cache.JCacheManagerCustomizer;
 import org.springframework.cache.annotation.EnableCaching;
+import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Profile;
 
@@ -11,4 +24,21 @@ import org.springframework.context.annotation.Profile;
 @EnableCaching
 @Profile("production")
 public class CacheConfig {
+
+    @Bean
+    public JCacheManagerCustomizer cacheManagerCustomizer() {
+        return new JCacheManagerCustomizer() {
+            @Override
+            public void customize(CacheManager cacheManager) {
+                CacheConfiguration<Object, Object> config = CacheConfigurationBuilder
+                    .newCacheConfigurationBuilder(Object.class, Object.class,
+                        ResourcePoolsBuilder.newResourcePoolsBuilder()
+                            .heap(100, EntryUnit.ENTRIES))
+                    .withExpiry(Expirations.timeToLiveExpiration(Duration.of(60, TimeUnit.SECONDS)))
+                    .build();
+                cacheManager.createCache("vets", Eh107Configuration.fromEhcacheCacheConfiguration(config));
+            }
+        };
+    }
+
 }