Consistently attach cause to exceptions.

Closes gh-713

Author: mp911de

spring-vault-core/src/main/java/org/springframework/vault/authentication/LoginTokenAdapter.java

@@ -90,7 +90,7 @@ private static Map<String, Object> lookupSelf(RestOperations restOperations, Vau
 		}
 		catch (HttpStatusCodeException e) {
 			throw new VaultTokenLookupException(String.format("Token self-lookup failed: %s %s", e.getStatusCode(),
-					VaultResponses.getError(e.getResponseBodyAsString())));
+					VaultResponses.getError(e.getResponseBodyAsString())), e);
 		}
 		catch (RestClientException e) {
 			throw new VaultTokenLookupException("Token self-lookup failed", e);

spring-vault-core/src/main/java/org/springframework/vault/authentication/VaultLoginException.java

@@ -61,7 +61,7 @@ public static VaultLoginException create(String authMethod, Throwable cause) {
 					String.format("Cannot login using %s: %s", authMethod, VaultResponses.getError(response)), cause);
 		}
 
-		return new VaultLoginException(String.format("Cannot login using %s", cause));
+		return new VaultLoginException(String.format("Cannot login using %s", cause), cause);
 	}
 
 }

spring-vault-core/src/main/java/org/springframework/vault/support/AbstractResult.java

@@ -82,7 +82,7 @@ public V get() {
 			return get0();
 		}
 
-		throw new VaultException(this.exception.getMessage());
+		throw new VaultException(this.exception.getMessage(), this.exception);
 	}
 
 	/**