[2404] lease_time renamed valid_lifetime in lease4 table

Make the names of the columns consistent between the lease4 and
lease6 tables.

src/lib/dhcpsrv/dhcpdb_create.mysql

@@ -34,7 +34,7 @@ CREATE TABLE lease4 (
     address INT UNSIGNED PRIMARY KEY NOT NULL,  # IPv4 address
     hwaddr VARBINARY(20),                       # Hardware address
     client_id VARBINARY(128),                   # Client ID
-    lease_time INT UNSIGNED,                    # Length of the lease (seconds)
+    valid_lifetime INT UNSIGNED,                # Length of the lease (seconds)
     expire TIMESTAMP,                           # Expiration time of the lease
     subnet_id INT UNSIGNED                      # Subnet identification
     ) ENGINE = INNODB;
@@ -77,7 +77,7 @@ CREATE TABLE schema_version (
     minor INT                               # Minor version number
     );
 START TRANSACTION;
-INSERT INTO schema_version VALUES (0, 1);
+INSERT INTO schema_version VALUES (0, 2);
 COMMIT;
 
 # Notes:

src/lib/dhcpsrv/tests/schema_copy.h

@@ -44,7 +44,7 @@ const char* create_statement[] = {
         "address INT UNSIGNED PRIMARY KEY NOT NULL,"
         "hwaddr VARBINARY(20),"
         "client_id VARBINARY(128),"
-        "lease_time INT UNSIGNED,"
+        "valid_lifetime INT UNSIGNED,"
         "expire TIMESTAMP,"
         "subnet_id INT UNSIGNED"
         ") ENGINE = INNODB",